Theme / styling with settings()

• Use classes like Svelte UX to pass class to underlying components
• Add createTheme() support
• Add .ComponentName classes
• Use const { format } = settings() / $format instead of formatNumber() / formatDate() directly
• Remove color prop (use rScale and fill / stroke / class / style?
  • Bars
  • Points
  • Pie
  • Link
  • Highlight
• Support design tokens (css variables) (see Svelte UX issue)
  • Should wait till the Svelte UX issue is resolved
• Remove all use of var(--color-xxx-xxx). Default to fill-accent-500 when possible (or possibly class="[--color:theme(colors.blue.500)]"

Start by reviewing the unchecked items in this issue and the referenced Svelte UX issue about design tokens. Identify the component entry points affected by classes, createTheme(), and settings() usage; the work is done when the remaining checklist items are implemented consistently and the existing color and design-token behavior remains supported.